A while back, I went to check out Tony's music shop in Taipei and noticed that they had this obviously home-made guitar pedal in the display case.
It was priced at NT$600nt (about US$20), and I was pretty much willing to pay that just for the parts I could use out of it.Anyway, I asked if I could try it out and they let me. It sounded superb.
There are two main amplifying components on it, a little 8-pin chip and a transistor.
The chip is marked:
OP275
And the transistor is marked:
C550B (This appears to be a BC550B)
There are three controls on it, labelled volume, tone and gain.
There are two toggle switches. The one on the side is a 3-way, with capacitors in 2 of the positions. It works as a tone filter I guess. At the back is a two-way switch, which appears to work as a kind of turbo overdrive.
Pot values are as follows:
VOLUME - A100K
TONE - B100K
GAIN - A50K (dual gang)
(A=audio taper, B=linear taper)
I traced the path of the dual-gang gain control. One gang connects between pins 1 and 2 of the OP275 and the other gang goes between pins 6 and 7 of the OP275. Shown below is an OP275. You can see that the gain control boosts BOTH amplifying stages at the same time. Serious boost there.
![](http://1.bp.blogspot.com/_10dB2S_qtCs/SQ6iJvaqU8I/AAAAAAAAAPg/ks9wo5hc16s/s320/op275.jpg)
The circuit appears to be something between a Big Muff Pi and a Rat, and despite requests on 3 different sites for information, it appears to be a totally unique design. If you know otherwise, please do let me know.
Here's a couple of pics of the guts:
incidentally, they dropped the price to NT$500 while I was paying for it. Happy days.
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